Female fruit flies fire up their immune systems before sex

Biologists at the University of St Andrews have discovered a
rather unromantic response in fruit flies to the prospect of sex --
the immune system of the female fires up in anticipation of an
invasion of bacteria and other nasties.

Professor
Michael Ritchie and his paper co-author Elina Immonen have
revealed in a paper in the Proceedings of the Royal Society:
Biological Sciences the expressions they found when studying
the genes of female drosophila melanogaster.

The study focused upon the power of a song produced by male
flies by vibrating their wings. The team first wanted to test the
specific effects of this song by exposing females to no song, a
synthetic song made to sound like it was produced by a different
species and one produced by their own species.

The female were played the different songs in the presence of
male flies; and the mating data then analysed. It was found that
the highest number of mating couples occurred when the "right" song
was played.

Next, however, was a study of the genetic response in the
females. Forty females at a time were placed in a chamber mounted
on a loudspeaker, then the three sounds were played again. The
females were then anaesthetising with CO2, snap-frozen with liquid
nitrogen and stored in -70 degrees celsius. The heads were then
removed from a total of 120 females and then an oligonucleotide
microarray (a chip that measures the expression of genes)
used to analyse the RNA from their brains.

Speaking to Wired.co.uk, Ritchie says that they identified
changes in three groups of the 14,000 genes present. The genes
affected were related to the flies' antennae, which the male song
causes to vibrate. Unexpectedly, there was also a response in the
females' immunity genes. Ritchie explains that they believe this is in
response to the fact that "when the female gets inseminated, the
process exposes her to bacteria and sexually transmitted diseases."
He adds that female flies that mate a lot tend to have shorter
lives than those that do not.

The University of St Andrews team is now working on a project in
which the specific genes known to be affected by the male song are
being manipulated. In particular, they are suppressing the
immunological response to see if this has an impact on the health
of the female flies -- presumably before they have their heads
chopped off.